The better alternative is to jailbreak your iphone and install ssh, a shell, python and many other free unix utilities you may want. I don't know why people are even voting this up.
1) It's my main form of communication 2) Apple killed jailbroken iPhones once, they could do it again 3) I can't afford to buy an un-subsidized 3G iPhone yet.
When any of those three changes, I'll jailbreak; 'til then, I'd rather pay a few bucks and keep warranteed reliability.